The present invention relates generally to printer ribbon cassettes, and, more specifically, to re-inking cassettes.
One type of printer ribbon cassette includes an endless ribbon disposed inside a cassette housing for being removably inserted into a corresponding printer. The ribbon is saturated with ink and is driven by the printer for cyclical use until the ink is depleted.
In order to ensure a suitable useful life, the cassette typically includes an inkwell having a foam insert or pad therein saturated with an additional volume of ink. A wick extends from the well and frictionally engages an ink wheel for continuously transferring ink from the well to the wheel, and in turn to the ribbon for replenishing the ribbon ink. In one embodiment, the ink wheel is in the form of a gear which cooperates with a mating gear, and between which is driven the ribbon in an endless loop. As the printer removes ink from the ribbon as each character is formed, the ink wheel resupplies the ribbon with ink removed from the well. In this way, each cassette may achieve a useful life typically expressed in millions of characters, such as five million for example.
Cassette life is the primary performance factor. This requires the ability to produce several million printed characters of suitable darkness. Insufficient or excess ink transfer to the ribbon during operation is undesirable since the former results in faded characters, and the latter may result in character smudging and possibly ink leaking from the cassette. Excessive ink transfer between the wick and ink wheel may accumulate ink on the wheel which falls by gravity to the bottom of the cassette and can leak through holes therein such as the bushing supporting the ink wheel itself.
Printer cassette Model No. 7141 manufactured and sold by the NCR Corporation is an example of a re-inking cassette enjoying commercial success for many years. Cassette performance and life are controlled in most part by the formulation of the ink used; the material and configuration of the foam ink pad and wick associated with the well; the configuration of the ink wheel; and the construction of the fabric ribbon. These components are interrelated in operation for ensuring the continuous re-inking of the ribbon as it travels through the cassette in repeated cycles for printing characters of acceptable darkness without premature character fading or ink leaking.
However, a statistically significant number of this exemplary cassette has failed to meet the desired minimum character life specification, and has led to the discovery of the present invention.